Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $109.51   8.617%   $118.9465   $118.95   $118.95   $118.90  
  Purchase #2 $26.95   11.392%   $30.0201   $30.02   $30.00   $30.00  
  Purchase #3 $58.54   11.300%   $65.155   $65.16   $65.15   $65.20  
  Purchase #4 $223.72   6.622%   $238.5347   $238.53   $238.55   $238.50  
  Purchase #5 $94.41   3.480%   $97.6955   $97.70   $97.70   $97.70  
  Purchase #6 $120.47   7.750%   $129.8064   $129.81   $129.80   $129.80  
  Purchase #7 $50.43   8.436%   $54.6843   $54.68   $54.70   $54.70  
  7 purchase totals = $684.03       $734.8425   $734.85   $734.85   $734.80